"At around midnight (2100 GMT Saturday), a group of security officers arriving in three cars, came and took Hassan al-Turabi from his home," his secretary Awad Babakir told AFP.

In a dawn raid later, authorities confiscated the newspaper of Turabi's Popular Congress Party (PCP) and arrested its editor-in-chief.

"After the arrest of the secretary general of the Popular Congress Party, security authorities stormed the printing house of the daily Rai Al-Shaab and confiscated all copies of the paper," said PCP politburo chief Kamal Omar.

"Authorities then took over the newspaper offices in central Khartoum and ordered all the journalists to leave."

The editor-in-chief, Abuzerr Ali al-Amin, told AFP by telephone he had been detained.

"At around 9:10 am (0610 GMT), a group of security and intelligence officials came to my house, put me in a car and took me to one of their offices," he said.

Two other journalists from the paper, Ashraf Abdel Aziz and Dahab Ibrahim, were also arrested, party officials said.

A pro-government press body said intelligence chief General Mohammed Atta al-Moula had suspended the paper's publication.

He "decided to put under supervision the press and information holdings of the Al-Nadwa company and its daily Rai Al-Shaab," the Sudanese Media Centre reported.

The information ministry said the action came after the paper published "erroneous" material.

"It published on its front page information claiming a serious conflict existed between Egypt and Sudan," and that engineers from Iran's Revolutionary Guards were in the country for a joint project, it said in a statement.

The government "is concerned about preserving liberties... but any flouting of the law will be punished."

Sunday's arrests sparked angry reactions from the opposition, who threatened to stage public protests and bring down the regime of President Omar al-Beshir.

"We will do everything we can within the law, sit-ins, demonstrations... We will embarrass this regime and expose it before the international community," Turabi's deputy Abdallah Hassan Ahmed told a news conference.

Some 300 PCP members gathered outside party offices chanting anti-government slogans and demanding the release of those arrested, an AFP journalist said.

A coalition of 17 opposition parties, including the heavyweight Umma party, signed a statement condemning Turabi's arrest as a "violation against freedoms and democratic transformation and the constitution."

The head of the Umma and last democratically elected president in Sudan, Sadiq al-Mahdi, arrived in Cairo on Sunday to discuss the situation after Turabi's arrest, sources told AFP.

The former southern rebel Sudan People's Liberation Movement -- partners in a coalition government -- also condemned Turabi's arrest.

"The arrest is outside the law, it is rejected. It is a violation of the constitution," SPLM senior member and former presidential candidate Yasser Arman, who withdrew from April elections before polling day, told AFP.

"After stealing the election, (the ruling National Congress Party) should not be stealing freedoms. This arrest exposes their weakness," Arman said. "Constitutional rights must be respected for Dr Turabi and others."

Turabi, once Beshir's mentor but now one of his fiercest critics, denounced last month's elections as fraudulent and said his party would not join a future government.

Beshir was declared winner with 68 percent of the vote in Sudan's first multi-party polls since 1986 which were marred by an opposition boycott, logistical problems and accusations of fraud.

Turabi, an iconic Islamist leader who has frequently been arrested, was last detained in January 2009, two days after he urged Beshir to surrender to the International Criminal Court.

In March 2009, the court issued an arrest warrant for Beshir over alleged war crimes and crimes against humanity in the war-torn western region of Darfur.

The seven-year conflict left 300,000 people dead, according to the United Nations. Khartoum says 10,000 were killed.